Furan fatty acids (F-acids) are a large group of fatty acids characterized by a furan ring, which carries at one α-position an unbranched fatty acid chain with 9, 11, or 13 carbon atoms and at the other α-position a short straight-chain alkyl group with 3 or 5 carbon atoms (1). Mostly two β-positions of the furan ring are substituted by either one or two methyl residues or other group. F-acid without any substitutions on both β-positions of the furan ring was also found in the seed oil of Exocarpus cupressiformis (2). F-acids are widely distributed in nature as trace components of plants, fishes, amphibians, reptiles, microorganisms and mammals including human (1, 3-7).
Although the biological role of F-acids in the biological system is not fully understood, it has been pointed out that F-acids can be involved in various important biological functions acting as antioxidant, antitumoral and antithrombotic (8-10). In some fishes F-acids comprised up to 25% of the acids in the liver lipids and accumulated during the spawning season indicating possible correlation between F-acids and the fertilization process (11). The correlation between consumption of fish rich in F-acid and protection against coronary heart disease mortality has been confirmed in several studies (12). F-acid has also been reported to have inhibitory effects on blood platelets aggregation (9) and to have potential antitumor activity (8). F-acids were found to prevent oxidation of linoleic acid (13) and act as antioxidants in plants (14). Some studies demonstrated that F-acids underwent oxidation by ring opening to form dioxoenes (15-16) in the presence of linoleic acid as co-substrate demonstrating that F-acid acted as a radical scavenger (17-18).
Biosynthesis of F-acids are complicated and quite different from sources. The biogenetic precursor of the most F-acids is known to be linoleic acid. It was recognized that plants synthesized the basic skeleton of F-acids from different sources (19). However, study with the radio-labeled feeding to fish indicated that fish synthesized neither the alkyl side chain nor the furan ring of F-acids (1). Therefore F-acids in fish were considered to be originated from diet, especially algae. Consequently F-acids are introduced into human body through the diet like vegetables and fishes. Diet-derived F-acid are incorporated into the tissue and blood of mammals, especially into phospholipids (20) where they might act as radical scavengers resulting into inhibition of blood platelet aggregation (9).
These reports indicated that F-acid could be an essential nutritional factor for mammals and could be used as an active component of functional food. However, no matter what biological sources of F-acids were, biosynthesis of F-acids required multistep reactions due to the formation of furan ring and the different alkyl substituents. Accordingly, chemical synthesis of F-acids required complicated multistep reactions and chemical catalysts causing difficulties and high costs for industrial application.
Recently we have produced 7,10-dihydroxy-8(E) octadecenoic acid (DOD) from vegetable oil containing oleic acid by microbial conversion (21). DOD is a dihydroxy monoenoic C18 fatty acid uniquely carrying two hydroxyl groups at carbon 7 and 10 and a trans double bond between carbon 8 and 9. Based on unique structural feature, it is highly plausible to modify DOD molecules by intra- or intermolecular interaction via chemical or physical ways. In our constant efforts to modify DOD for biological and industrial applications, we developed a simple way to produce a novel biologically active F-acid from DOD through one-step heat treatment.